Forestry & Forest Sciences · Forest Products & Utilization · also Logging and Ergonomics, Forest Engineering, Timber Harvesting and Transport
Getting wood from stump to mill safely and with least damage: harvest planning, felling and extraction systems, forest roads, transport, ergonomics and reduced-impact logging. The Agricultural Engineering track (aquacultural-forest-engineering) introduces roads and logging machinery in a few units; this subject treats forest operations in full.
In the exams: IFoS Forestry Paper II Section A (surveying and forest engineering); ICAR AICE-JRF 59 Unit 7 (logging and ergonomics); PRC Forest Engineering and Utilization; Korea Forestry Engineer written subject Forest Road Engineering; ICAR AIEEA-PG Group 09 (forest engineering)
Forest operations turn silvicultural prescriptions into work on the ground: felling trees, moving them to roads, building and maintaining the roads, transporting logs to mills, and doing all this safely, economically and with the least damage to the soil, water and remaining forest. Harvesting is usually the most expensive and the most environmentally consequential operation in a managed forest. It decides how much of the tree's value reaches the market, whether regeneration survives, whether streams stay clear and whether workers go home uninjured. Forest engineering is the branch of forestry that plans and designs these operations and the infrastructure, especially roads, bridges and extraction systems, on which they depend.
This subject covers harvest planning and layout; felling by hand, by chainsaw and by machine, including directional felling; chainsaw use and safety; extraction by skidding, forwarding, cable systems, animals and aircraft; harvesting systems such as cut-to-length and whole-tree; forest road planning, location and grades; road construction, drainage and maintenance; timber transport by road, water and rail; log scaling, sorting and landing operations; ergonomics and occupational safety in forest work; reduced-impact logging and soil protection; and forest bridges and simple structures. The Agricultural Engineering track's aquacultural-forest-engineering subject introduces forest roads and logging machinery in a few units under the Philippine engineering law; this subject treats forest operations in full. Related subjects cross-referred rather than repeated are: farm-machinery-management, tractor-systems-controls and ergonomics-safety in the Agricultural Engineering track (machine costs, tractor systems and general ergonomics); forest-mensuration (log volume formulas); wood-anatomy-properties and wood-seasoning-preservation (log quality, storage and protection); and forest-hydrology-watershed (road drainage and riparian buffers).
Forest operations are examined in Section A of Paper II of the Indian Forest Service forestry optional (surveying and forest engineering), in Unit 7 of the ICAR AICE-JRF forestry syllabus (logging and ergonomics), in the ICAR AIEEA-PG forestry group (forest engineering), as Forest Engineering and Utilization in the Philippine Foresters licensure examination, and as Forest Road Engineering in Korea's Forestry Engineer qualification. Questions ask for felling techniques and safety, the merits of extraction and harvesting systems, road classification, grades and drainage, scaling methods, ergonomic hazards and the principles of reduced-impact logging, with simple calculations of grades, road density and extraction distance.
Harvest planning works at three levels. Strategic planning, within the forest management or working plan (see working-plans-planning), decides how much is harvested over the plan period, from which compartments and by which silvicultural system, and plans the main road network. Tactical planning, for the next one to five years, sequences harvest units, schedules road construction and allocates equipment and contractors. Operational planning prepares the detailed harvest plan for each unit, often called the logging plan, which guides the crews on the ground.
An operational harvest plan is based on a pre-harvest inventory and a map at a suitable scale showing topography (contours), streams, wet areas, steep or unstable slopes, protected areas and buffers, existing roads, and the trees to be felled and retained. In selective systems, trees to be harvested are marked by species, diameter and quality, along with future crop trees, seed trees and protected trees to be retained. The plan then locates landings (log decks, where logs are collected for loading), skid trails or extraction routes, road extensions, stream crossings and directions of felling, and it specifies the extraction system, equipment, timing, safety arrangements and environmental safeguards. Planning skid trails in advance, rather than letting operators choose routes as they go, is one of the most effective ways of reducing soil damage and cost.
Timing affects cost, safety and damage. Operating on dry or frozen ground reduces soil compaction and rutting; avoiding wet seasons protects roads and streams; avoiding bird breeding seasons or regeneration periods may be required; and felling in the dormant season can reduce bark damage and stain in some species. Many harvests are carried out by contractors under contracts that specify the work, standards, safety requirements, environmental conditions, payment basis (per cubic metre, per tonne or per hour) and penalties for damage, with supervision and post-harvest inspection by the forest owner or agency. In India, timber harvesting in government forests is often done departmentally or through forest development corporations, and logs are sold at depots by auction.
Planning requires estimates of productivity (volume per productive machine hour or per worker-day) and costs for each operation. Productivity depends on tree size (larger trees give higher productivity per cubic metre), stand density, terrain (slope, ground roughness and bearing capacity), extraction distance, operator skill and the system used. Machine costs per hour include ownership costs (depreciation, interest, insurance) and operating costs (fuel, lubricants, maintenance and repairs, labour), calculated by methods similar to those used for farm machinery (see farm-machinery-management in the Agricultural Engineering track). Time studies, which record the time taken for each work element, are used to model productivity and set fair contract rates.
Felling can be manual, using axes and crosscut or bow saws; motor-manual, using chainsaws; or mechanised, using machines. Manual felling is still used in some places for small trees and where chainsaws are unavailable, but it is slow and physically demanding. Motor-manual felling with the chainsaw is the most widespread method worldwide, flexible across tree sizes and terrain. Mechanised felling uses feller-bunchers, which cut trees with a shear, disc saw or bar saw and gather them into bunches for skidding, and single-grip harvesters, which fell, delimb, measure and cross-cut trees into logs at the stump with a harvester head on a boom. Mechanised felling is much safer and more productive in suitable stands and terrain, but needs high investment, skilled operators and trees within the size range of the machine.
Directional felling controls the direction in which a tree falls, to protect workers, avoid damage to the felled tree, residual trees and regeneration, keep trees out of streams and place them conveniently for extraction. The basic technique uses three cuts. The notch (face cut or undercut) is cut on the side facing the intended direction of fall, to a depth commonly of about one-quarter to one-third of the stump diameter; its opening angle may be the conventional notch of about 45° or the open-face notch of 70° or more, which keeps the hinge working longer as the tree falls. The back cut (felling cut) is made from the opposite side, horizontally and at or slightly above the apex of the notch, stopping short to leave a strip of uncut wood, the hinge (holding wood), commonly about one-tenth of the diameter in thickness and running the full width of the notch. The hinge guides the tree as it falls and must never be cut through. Felling wedges or levers driven into the back cut push the tree over and prevent the saw from being pinched.
Trees that lean, have heavy one-sided crowns, are hollow or rotten, have buttresses, or are hung up in other trees require special techniques and experience. Leaning trees can split vertically (barber chair) if the back cut is made too slowly; techniques such as boring cuts and bypassing the hinge sequence reduce this risk. Buttresses are trimmed before felling. Hung-up trees must never be climbed or cut under; they are brought down with winches, levers or by rolling, with everyone clear of the danger zone. Dead trees (snags) are dangerous because dead branches and tops can fall without warning.
Before felling, the feller checks the tree for lean, defects and hazards such as dead branches, clears brush around the base, and plans and clears two escape routes, usually diagonally back from the direction of fall at about 45° on either side. No one other than the feller should be within a distance of at least two tree lengths from the tree being felled. After the tree begins to fall, the feller moves away along an escape route and watches the crown. These rules are taught in training and certification programmes for chainsaw operators.
The chainsaw is a portable power saw with a cutting chain running around a guide bar, driven by a two-stroke petrol engine, or increasingly by battery-electric motors for smaller saws. The cutting chain has cutters with a cutting edge and a depth gauge (raker) in front of each, which limits how deep each cutter bites; correct filing of cutters and adjustment of depth gauges keep the chain cutting efficiently and safely. A blunt chain makes the operator press harder, increases fatigue and vibration and raises the risk of accidents.
Modern chainsaws have several safety features: a chain brake, activated by a front hand guard or by inertia in kickback, which stops the chain within a fraction of a second; a chain catcher that catches a broken or derailed chain; a rear hand guard protecting the right hand; a throttle trigger lockout preventing accidental acceleration; an anti-vibration system isolating the handles from the engine; a stop switch within easy reach; and a muffler and spark arrester. These must be checked before every use.
Kickback is the sudden upward and backward movement of the guide bar towards the operator that occurs when the chain at the upper part of the nose of the bar (the kickback zone) contacts an object or gets pinched. It is a leading cause of serious chainsaw injuries, especially to the head and neck. Avoiding cutting with the upper nose of the bar, holding the saw firmly with both hands with thumbs wrapped around the handles, keeping the saw below shoulder height and using low-kickback chains reduce the risk. Other hazards include contact with the running chain, being struck by falling trees or branches, pull-in and push-back when the chain is pinched, noise (chainsaws commonly exceed 100 dB), vibration causing hand-arm vibration syndrome (vibration white finger), exhaust fumes, burns and fire from refuelling, and fatigue.
Personal protective equipment for chainsaw work includes a safety helmet with face screen (mesh visor) and ear protection, protective trousers or chaps containing layers of long fibres that clog the chain and stop it when cut, chainsaw boots with steel toecaps and cut-resistant fronts, protective gloves and high-visibility clothing. Good practice includes starting the saw on the ground or held firmly with the chain brake on, refuelling with the engine off and away from the work area, never working alone in felling, carrying a first-aid kit including treatment for severe bleeding, taking regular breaks, and maintaining the saw daily. Training and certification of chainsaw operators, as required in many countries, sharply reduce accidents.
Extraction (primary transport or yarding) moves felled trees or logs from the stump to a landing or roadside. In skidding, logs are dragged along the ground, with one end raised or not, by a cable skidder (which winches logs to it with a chokers-and-cable system), a grapple skidder (which picks up bunches with a hydraulic grapple), a crawler (tracked) tractor, or a farm tractor fitted with a winch. Skidding is cheap and versatile, but dragging logs disturbs and compacts soil, damages residual trees and soils logs with dirt that dulls saws. It is generally limited to gentle and moderate slopes; steeper ground requires cable systems or other methods, and limits depend on soils, equipment and regulations.
A forwarder is a self-loading vehicle that carries logs completely off the ground in a bunk, loaded with a hydraulic crane. Forwarding is the extraction part of the cut-to-length system: logs processed at the stump by a harvester or chainsaw are picked up and carried to roadside. Because logs are carried rather than dragged, forwarding causes less soil disturbance and keeps logs clean, and forwarders with wide tyres, bogie tracks and low ground pressure can travel on softer ground than skidders. Forwarders are widely used in Europe and increasingly in plantations elsewhere.
Cable (skyline) systems use a yarder, a machine with winches and a tower, to pull logs to a landing on wire ropes, either with one end suspended (partial suspension) or fully suspended above the ground. They are used on steep slopes where ground-based machines cannot operate safely, and they cause much less soil disturbance on slopes than tractors. In highlead systems, a main line and haulback line pass through a block high on the tower and logs are dragged with their front end lifted. In skyline systems, a fixed or running skyline cable is stretched between the tower and an anchor (tailhold), and a carriage running on it carries logs with partial or full suspension. Cable systems require careful layout of cable corridors, anchors and landings, skilled crews and higher costs.
Animal extraction uses elephants (traditionally in India, Myanmar and Thailand for teak and other heavy logs), buffaloes, oxen, horses and mules. It causes little soil damage, needs little infrastructure and suits small-scale, selective harvesting, steep or sensitive sites and community forestry, but productivity is low and animals require care and skilled handlers. Manual extraction by carrying, rolling or sliding small logs is still used for fuelwood and poles. Timber slides and chutes have been used in the Himalaya to move logs down steep slopes, and floating and rafting on rivers once moved large volumes of timber (see the transport chapter). Helicopter logging lifts logs from areas with no road access or high environmental sensitivity; it is very expensive and used mainly for high-value timber or salvage. Balloon logging was tried in a few places.
A harvesting system is the combination of machines, methods and the form in which wood is moved from the stump to the roadside or mill. Systems are classified by where trees are processed (delimbed, topped and cross-cut) and in what form they are extracted: as logs, as stems or as whole trees. The choice depends on tree size, terrain, products, markets for residues, environmental requirements, labour costs and available capital and skills.
In the cut-to-length (CTL) or shortwood system, trees are felled, delimbed, topped and cross-cut into logs of specified lengths at the stump, either by a single-grip harvester or by chainsaw, and the logs are extracted by forwarder to the roadside. Branches and tops remain in the stand, often laid as a brush mat on the machine trails, which protects the soil and returns nutrients. The system allows careful thinning with little damage, produces clean, sorted logs, and needs fewer machines at the landing. It is dominant in the Nordic countries and widely used in thinnings and plantations elsewhere. It is less suited to very large trees and steep terrain.
In the whole-tree system, trees are felled, often by feller-bunchers, and extracted whole, with branches and tops, by grapple skidders to the roadside or landing, where they are delimbed, topped and cross-cut by processors or delimbers. In the tree-length system, trees are delimbed and topped at the stump and the stems are extracted in full length for cross-cutting at the landing or mill. Whole-tree systems achieve high productivity with large, mechanised operations, as in the southern United States, and concentrate branches and tops at the landing, where they can be chipped for energy. However, they remove more nutrients from the site, need large landings, and dragging whole trees can cause more soil disturbance and residual damage.
In practice, systems are often mixed and adapted. In India, most felling is motor-manual, with logs extracted by tractors, trucks, animals or manual labour, and cross-cutting often done in the forest before extraction to depots; mechanised systems are used mainly in some plantations. Considerations in choosing a system include the size and form of trees, slope and soils, the silvicultural system (thinning versus clear felling), product mix, need to retain or remove residues, worker safety, environmental standards and certification requirements, and the cost of labour relative to machines.
Forest road networks are usually classified by function and standard. Primary (main or trunk) roads connect the forest to public roads and carry traffic from large areas all year round; they have the highest standard, with wide carriageways, all-weather surfacing and permanent bridges. Secondary roads branch from primary roads to serve parts of the forest. Tertiary roads (spurs) reach individual harvest units, are of lower standard and may be used only seasonally or temporarily. Skid trails and forwarder trails are not roads but extraction routes. The network as a whole should provide access for harvesting, silviculture, fire protection and management at the least total cost of construction, maintenance, transport and extraction.
Road density is the length of road per unit area, often expressed in metres per hectare. For a forest served by parallel roads at a spacing of S metres, road density is 10 000 ÷ S metres per hectare; roads 400 m apart give 25 m/ha. With logs extracted to both sides, the average extraction distance is about S ÷ 4, or 100 m at 400 m spacing. Closer road spacing reduces extraction distance and cost but increases road construction and maintenance costs, so there is an optimum road spacing that minimises the sum of road and extraction costs; it depends on the cost of road per metre, the extraction cost per cubic metre per unit distance and the volume harvested per hectare. Cheap extraction (such as skidding) and low harvest volumes favour wider spacing; expensive extraction (such as cable systems) and high volumes favour denser networks. Roads also have environmental costs, so minimising road length within operational needs is desirable.
Road location is planned first on maps and aerial imagery, increasingly with geographic information systems and digital elevation models, and then confirmed and marked on the ground. Good locations follow gentle grades, use ridges, benches and gentle side slopes, avoid streams, wetlands, unstable slopes and erodible soils, minimise stream crossings and cross streams at right angles at stable points, keep away from riparian buffers (see forest-hydrology-watershed), place landings on well-drained ground, and serve the harvest units efficiently. Grade control points, such as saddles, stream crossings and junctions, are identified first, and the route is laid out between them at acceptable grades.
Road grade (gradient) is the vertical rise divided by horizontal distance, expressed as a percentage: a rise of 12 m over 150 m horizontal distance is an 8% grade. Grades affect vehicle speed, fuel use, braking, safety and erosion. Favourable grades (downhill for loaded trucks) can be steeper than adverse grades (uphill for loaded trucks). Typical design limits for forest roads are a maximum sustained grade of the order of 8–10%, with short pitches steeper where necessary, but standards vary by road class, vehicle type and climate, and very flat grades (below about 2%) make drainage difficult. Horizontal curves must be wide enough for long log trucks to turn, with widening on curves, and adequate sight distances for safety.
Forest road construction begins with clearing the right-of-way of trees and vegetation, removing stumps and topsoil from the roadbed, and then earthworks: cutting into the slope on the uphill side and placing fill on the downhill side to form a level or gently sloping roadbed. Balancing cut and fill along the route reduces haulage of material. On steep slopes, full-bench construction (cutting the whole road width into the slope and hauling away excess material) avoids unstable fill. The subgrade is compacted, and a base and surfacing of gravel or crushed rock are placed where traffic and wet seasons require them; low-standard spur roads may be left unsurfaced. Excavated material must not be sidecast into streams or onto unstable slopes.
Water is the main cause of road failure and road-related erosion, so drainage is the most important part of road design. The road surface is shaped to shed water: crowned (sloping to both sides), insloped (towards a ditch on the uphill side) or outsloped (towards the downhill side, dispersing water over the slope). Side ditches carry water along the road and must be relieved frequently by cross drains, culverts (pipes or boxes under the road) or rolling dips (gentle undulations that turn water off the road), with spacing decreasing as grade increases. Outlets must discharge onto stable, vegetated ground or protected aprons, never onto fill slopes or directly into streams. Stream crossings require culverts or bridges sized to pass flood flows and debris and, where needed, fish; culvert sizing uses design flood estimates (see the hydrology subjects in this track and the Agricultural Engineering track). Water bars, earth ridges angled across the road or trail, divert water from closed roads and skid trails.
Roads deteriorate quickly without maintenance. Routine maintenance includes grading the surface to restore its shape and remove ruts, cleaning ditches and culvert inlets and outlets, removing slides and fallen trees, controlling roadside vegetation, replacing surfacing and repairing damaged structures. Inspections after storms catch blocked culverts before they cause washouts. Restricting heavy traffic during wet periods, when surfaces are soft, prevents rutting and sediment production. Roads that are no longer needed may be closed, with drainage structures that function without maintenance (water bars, outsloping) or decommissioned by removing culverts, restoring stream crossings and revegetating the road surface.
Roads can be the largest source of sediment from managed forests, and they fragment habitats, open access for illegal logging, hunting and settlement, and can trigger landslides on steep slopes (see forest-hydrology-watershed). Good location, minimal road length, sound drainage, prompt revegetation of cut and fill slopes, careful stream crossings and timely closure greatly reduce these impacts. Best management practices for forest roads are central to forest certification and to the protection of water supplies.
Most timber today moves by road, on log trucks with rigid bodies, truck-and-trailer combinations or articulated tractor-semitrailers with stakes or bunks to hold logs. Self-loading trucks with mounted cranes are common in Europe and plantation operations. Transport costs depend on distance, road standard, payload, truck type, loading and unloading time and backhaul opportunities, and are commonly compared per tonne-kilometre or per cubic metre-kilometre. Legal axle and gross vehicle weight limits must be observed; overloading damages roads and bridges and causes accidents. Transport is often the largest single cost in delivering wood to a mill, so mill location, road standards and logistics planning have major economic effects. In India, transport of timber requires transit passes under state transit rules, which are used to control illegal movement (see forest-policy-law-governance).
Before roads, rivers were the main means of moving timber. Logs were floated individually down rivers during high water (log driving), assembled into rafts on larger rivers, and collected at downstream booms and depots. In India, rivers such as the Ganga, Yamuna, Chenab and others in the Himalaya and rivers in the Western Ghats were used to float timber, and teak from Myanmar was famously floated down the Irrawaddy and its tributaries. Floating requires logs light enough to float (one reason for girdling teak before felling) and causes losses through sinking, stranding and damage, as well as environmental impacts on rivers. Barges and ships carry logs and processed products on rivers, lakes and seas, and international trade relies on bulk carriers and container shipping.
Forest railways and tramways were built in many forests in the late nineteenth and early twentieth centuries, including in India, to carry timber from remote forests to markets; most have since closed, though some survive as heritage lines. Rail remains important for long-distance transport of logs, pulpwood and products in countries such as Canada, Russia and Sweden. Ropeways (aerial cableways) were used to move timber across valleys in mountainous areas. The choice of mode depends on distance, volume, infrastructure and cost; combinations (truck to rail or port) are common.
Modern wood supply chains use planning systems that match harvest scheduling to mill demand, track loads by GPS and electronic delivery notes, minimise empty running, and coordinate harvesting, transport and mill intake. Measuring loads by weight at mill weighbridges, with conversion factors to volume, is widespread. Good logistics reduces cost, inventory, deterioration of logs in storage and the carbon footprint of transport.
Scaling is the measurement of the quantity of wood in logs for sale, payment of contractors, royalty assessment and inventory control. Logs are measured for length and diameter (or girth), and volume is calculated by formulas such as Huber's or Smalian's (see forest-mensuration), or read from log volume tables. In India, round timber has traditionally been measured by mid-girth and length, with volume computed by the quarter-girth (Hoppus) rule or by true volume, depending on the sale conditions. In North America, log rules estimate the sawn output in board feet rather than solid volume. Scaling standards specify measurement points, rounding, and deductions for defects such as rot, splits, sweep and crook, so that the net scale reflects usable volume. Weight scaling, weighing trucks at the mill, is common for pulpwood and plantation logs, with conversion to volume by measured density factors.
Bucking (cross-cutting) divides stems into logs. Because the value of logs depends on their length, diameter and quality, how a stem is bucked can change its total value considerably. Bucking optimisation chooses cutting points to maximise value given price lists and specifications, considering defects such as knots, sweep and rot; it is done by trained buckers or by computers on harvesters, which measure the stem as it is processed and calculate optimal cuts. Logs are then graded by quality (for example veneer, sawlog, peeler, pulpwood) according to grading rules that consider diameter, length, straightness, knots and defects.
At the landing or roadside, logs are sorted by species, grade and length into separate decks, measured, marked and loaded onto trucks. Landing work may include delimbing, topping, bucking, debarking and chipping, depending on the system. Landings should be on stable, well-drained sites outside riparian zones, of adequate size for the operations, and rehabilitated after use. Safety at landings is critical, because machines, moving logs and people work close together.
In Indian forestry, timber is often transported to departmental or corporation depots, where logs are measured, graded, marked with property marks (hammer marks) and numbers, arranged into lots and sold by auction or tender (see forest-economics-valuation for stumpage). Records of lots, volumes and prices are maintained, and transit passes are issued for removal. Protecting logs in depots from stain, decay and insects (see wood-seasoning-preservation) preserves value, especially for non-durable species in warm, humid climates.
Forestry work, especially felling and extraction, is one of the most dangerous occupations in many countries, with high rates of fatal and serious injuries. The main causes of fatal accidents are being struck by falling trees, branches or rolling logs, chainsaw injuries, machine accidents (rollovers, being struck by moving parts or loads) and vehicle accidents. Non-fatal injuries include cuts, sprains, fractures and back injuries, and long-term health effects include hearing loss, vibration-induced disorders and musculoskeletal problems. The International Labour Organization has issued a code of practice on safety and health in forestry work that sets out principles for employers, workers and authorities.
Ergonomics adapts work to human capabilities. Manual forest work, such as felling with hand tools, carrying and stacking, is heavy work with high energy expenditure, measurable by heart rate and oxygen consumption, and hot climates add heat stress. Work-rest schedules, adequate food and water, rotation of tasks, good tools (correctly sharpened and suited to the worker) and teamwork reduce fatigue and injuries. For motor-manual work, vibration, noise and awkward postures are the main concerns; for machine operators, whole-body vibration, repetitive movements, mental workload, sitting for long periods and cab design (visibility, seat, controls, climate) matter. General principles of agricultural ergonomics and safety are covered in the Agricultural Engineering track's ergonomics-safety subject.
Forest machines must have protective structures: roll-over protective structures (ROPS) to protect the operator if the machine overturns, falling object protective structures (FOPS) against falling trees and branches, and operator protective structures (OPS) against penetrating objects such as broken cable or saw chain. Machines should be operated within their slope limits, with seat belts, and with other workers kept outside the danger zone. Cable systems require trained crews, clear signals, safe positions away from the bight of moving lines and regular inspection of ropes and anchors. Agricultural tractors adapted for forestry need appropriate guards and protective structures (see tractor-systems-controls in the Agricultural Engineering track).
Safety depends on organisation as much as equipment: risk assessment of each worksite, written safe work procedures, training and certification of workers (especially chainsaw operators and machine operators), supervision, provision and use of personal protective equipment, first-aid training and kits, emergency plans for evacuation of injured workers from remote sites, communication equipment, limits on working hours, fair payment systems (piece rates that encourage rushing increase accidents) and accident recording and investigation. Contractors and their workers must be included. Certification standards for forest management require attention to worker safety and rights.
Reduced-impact logging (RIL) is a set of planned and controlled harvesting practices designed to reduce damage to the residual stand, soil, water and biodiversity, and waste of timber, compared with conventional, unplanned logging, particularly in tropical natural forests. It was promoted in the FAO Model Code of Forest Harvesting Practice (1996) and in regional codes for the Asia-Pacific and other regions, and its adoption is required by many certification standards and concession regulations. RIL is not a single technique but a package of practices applied before, during and after harvest.
Before harvest, RIL requires a pre-harvest inventory and mapping of all harvestable and future crop trees, streams and topography; planning of roads, skid trails and landings on the map; cutting of climbers (vines) linking crowns, ideally six months or more before felling, so that felled trees do not pull down neighbours; and setting minimum diameter limits and retention of seed trees and protected species. During harvest, directional felling places trees to minimise damage and ease extraction; skidders stay on planned trails, and logs are winched to the trail rather than the machine driving to each stump; operations stop in wet weather; and stream buffers are respected. After harvest, skid trails and landings are closed and drained, and the operation is assessed. Studies in tropical forests have shown that RIL substantially reduces damage to residual trees, soil disturbance and wasted timber, and can reduce carbon emissions from logging, while maintaining or improving productivity.
Machine traffic compacts soil, reducing pore space, infiltration and aeration, and impeding root growth; it also causes rutting, displacement of topsoil and erosion. Damage is greatest on wet, fine-textured soils and with repeated passes; most compaction occurs in the first few passes of a machine. Recovery can take decades. Compaction on skid trails and landings can reduce growth of the next crop and increase runoff.
Soil protection measures include confining traffic to designated trails and landings, at a planned spacing, rather than allowing machines to travel freely; operating when soils are dry or frozen; using low ground-pressure machines with wide tyres, bogie tracks or tracks; laying brush mats of branches and tops on machine trails (as in cut-to-length systems); limiting the number of passes; avoiding steep slopes with ground-based equipment; and rehabilitating trails by ripping (subsoiling), water barring and revegetation after use. Cable and animal extraction cause less soil disturbance on sensitive sites. Monitoring of soil disturbance after harvest is part of best management practices and certification audits.
Stream crossings are the most sensitive and expensive points on forest roads. Options include fords (low-water crossings), culverts and bridges. The choice depends on stream size and flow regime, the frequency and size of floods, fish passage requirements, traffic, the life of the road, cost and environmental impacts. Poorly designed crossings can wash out, block fish movement, cause erosion and deliver sediment directly into streams. Crossings should be at right angles to the stream, at narrow, stable sections with firm banks, and approaches should be drained so that road runoff does not enter the stream.
Culverts are pipes or boxes of corrugated steel, concrete or plastic that carry water under a road. They must be large enough to pass the design flood and debris, installed at the natural stream gradient and bed level, bedded and backfilled properly, protected at the inlet and outlet against erosion, and kept free of blockage. For fish-bearing streams, culverts should be embedded or replaced by open-bottom arches or bridges so that the natural streambed continues through the crossing. Fords and low-water crossings, often with concrete or stone surfaces, suit streams that are dry or shallow most of the year and roads with low traffic; they avoid the risk of blocked culverts but are impassable during floods.
Forest bridges range from simple log stringer bridges, made of large logs laid across the stream on abutments and decked with timber, to engineered bridges of sawn or glued-laminated timber, steel girders with timber decks, concrete, and modular prefabricated steel bridges (such as panel bridges), which can be assembled quickly and moved. Bridge design considers span, design loads (the heaviest expected log trucks and equipment, with safety factors), abutments founded on stable ground or rock above flood level, scour protection, clearance above flood flows and debris, durability of materials (treated or durable timber, see wood-seasoning-preservation) and maintenance. Temporary portable bridges are used for skid trail crossings to avoid fording.
Other structures in forest engineering include retaining walls (dry stone, gabion or crib walls) to support cuts and fills on steep slopes; drainage structures such as drop inlets, armoured ditches and energy dissipators; cattle grids and gates; and timber slides, chutes and ropeways for extraction in mountain areas. Simple, robust structures built of local materials, such as stone, logs and gabions, are often appropriate in forest settings, but they must be designed and inspected by competent people, since failures can endanger lives and cause environmental damage.
Learn the sequence of a harvest plan, directional felling cuts and safety rules, the features of each extraction method and harvesting system and where each fits, road classes, the meaning of grade and how to calculate it, road density and extraction distance, drainage principles, scaling methods and log grading, the main ergonomic hazards and protective structures, and the elements of reduced-impact logging. Practise simple calculations and be ready to compare systems in descriptive answers.
A forester five years in prepares harvest plans and maps, marks trees, lays out skid trails, landings and roads, supervises felling and extraction crews or contractors, checks safety practices and equipment, enforces environmental conditions, measures and grades logs at landings and depots, organises transport and transit passes, and inspects roads and crossings after storms. Practical skills include map and GPS use, reading terrain, supervising chainsaw work, scaling and record-keeping.
A senior forester sets standards and policies for forest operations: road network planning and investment, codes of harvesting practice and reduced-impact logging, mechanisation strategy, contractor systems and safety management, timber sale and depot systems, and compliance with certification and environmental regulations. The senior forester balances costs, safety, environmental impacts and community concerns and responds to major events such as storms that require salvage operations.
A senior researcher studies harvesting productivity and costs, machine-soil interactions and soil recovery, ergonomics and accident prevention, road network optimisation and hydrological effects, bucking and supply-chain optimisation, precision forestry with sensors on machines, and the outcomes of reduced-impact logging for forests and carbon; contributes to codes of practice and standards; and trains forest engineers.
Design standards (road widths, grade limits, curve radii, culvert sizes, bridge loads) vary by country, road class and vehicle and are given only as typical values; engineering design must follow national standards and competent design. Slope limits for ground-based machines and notch and hinge proportions are typical guidance taught in training, not universal rules. Machine productivity and cost figures are not given. Detailed cable logging layout and payload analysis, bridge structural design and culvert hydraulics are outside the scope. Machine costing methods are in farm-machinery-management and tractor systems and general ergonomics in the Agricultural Engineering track; log volumes in forest-mensuration; log protection in wood-seasoning-preservation; and road hydrology in forest-hydrology-watershed.
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